The present invention relates generally to the field of magnetic tape drives for recording of data, and more particularly, to techniques for detecting end-of-tape and beginning-of-tape conditions. In some types of tape drives, data are recorded in multiple parallel tracks along the tape, to increase the recording density. For data recording, two tape markers are required at each end of the tape.
An end-of-tape marker is positioned close to the physical end of the tape, to signal the end of the usable area of the tape and to prevent removal of the tape from its spool. In addition, a warning marker is needed some distance before the end-to-tape marker. When the warning marker is encountered, recording can be appropriately terminated by writing a block of information, referred to as a postamble, before reaching the end of the usable area of the tape. The same two types of markers are also provided near the other end of the tape, since half of the tracks in multiple-track tapes are recorded in one direction and the other half of the tracks are recorded in the other direction. The warning markers actually serve a dual purpose in some tape controllers. Before starting to record on track, the controller must first detect the marker used as a warning marker when recording in the opposite direction. When encountered at the beginning of a recording track, the marker identifies a tape load point and recording is not initiated until the load point is reached.
The end-of-tape and beginning-of-tape markers are typically formed as holes through the tape material. The hole positions can then be sensed optically or by electrical means. In tape drives of the prior art, there are typically no more than four parallel recording tracks on a tape one-quarter-inch wide. The warning or load-point markers are formed as small holes positioned between two adjacent recording tracks. Although this arrangement has been generally satisfactory, it significantly limits the number of parallel tracks that can be accommodated on the tape. The present invention was conceived to allow warning markers to be incorporated onto a tape having up to twenty-four tracks and having a width of only one-quarter of an inch.